RF #'s vary greatly from patient to patient. it's not a real deciding factor for disease and shouldn't be used to diagnose all by itself.
also...a RF won't "tell you" how bad say for example a person's RA is.
wheni was 20 y/o...my RF was well over 130...and my RA was not as bad as it was NOW. recently, my last RF level was like 50 or 60 something, and the RA is at a disabling point.
a positive RF can be present in a SLEW of illnesses....even "normal" people can have an RF level (the ellderly usually do).
a pt. can also have an RF level after a broken bone as well.
your RF number is just an antibody that floats around in the blood of many people who do in fact have Rheumatory Arthritis.
*RF is not exclusive to just Rheumatoid Arthritis...a Rheumatoid Factor (RF) can show up in folks with: SLE, lupus; TB; scleroderma; endocarditis; Sjogrens syndrome; sarcoidsis; cancer; Syphylis & viral infections like Epstein-Barr.
in all, docs use the RF test in bloodwork because the values of RF is often quite higher in people who do have RA.
it's just useful in trying to get a diagnoses. RF supports a tentative diagnoses of RA...but used alone, is not enough to make a diagnoses of RA.
*nomal values are usually 0-20 U/mL give or take a few depending on the lab (all labs have a tendency to vary a point or 2)
*an absent RF does not exclude Rheumatory Arthritis.
so they'll use this test, plus your statements of symptoms, pain levels in joints, swelling, symmetrical joint pain & swelling & stiffness, RA nodules if present, and XRAY changes of the joint or decalcifications/deformities, & family history.
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